Means for bounding cushion spaces of gas cushion vehicles

ABSTRACT

The cushion of a gas cushion vehicle is contained by a wall structure comprising a horizontal row of rigid members of lamellar form, e.g., discs, mounted for independent vertical movement with respect to each other. The lower surfaces of the members are curved to define a convergent-divergent passage between them and the surface over which the vehicle is to operate, for the escape of gas from the cushion. The members are preferably enclosed in a downwardly open chamber, separate from the cushion space. In use, by suitably controlling the pressure above the members, e.g., in the chamber, the aerodynamic forces exerted on the members due to the flow of cushion gas beneath them, are arranged to maintain the members in an equilibrium position spaced above the surfaces over which the vehicle operates.

United States Patent Spillman [54] MEANS FOR BOUNDING CUSHION SPACES OFGAS CUSHION VEHICLES [72]- lnventor: John James Spillman, Bedford,England [73] Assignee: National Research Development Corporation,London, England [22] Filed: March 30, 1970 [21] Appl. No.: 23,829

[30] Foreign Application Priority Data April 2, 1969 Great Britain..l7,244/69 [52] US. Cl ..180/127 [51] Int. Cl ..B60v 1/00 [58] Field ofSearch ..130/126, 127, 128

[56] References Cited UNITED STATES PATENTS 3,204,715 9/1965 Maloof..180/126 3,288,236 11/1966 Padial ..180/126 3,330,369 7/1967 Hayward..180/127 Hopkins et a1 l 80/127-X Francis et a1. ..180/127 PrimaryExaminer-Kenneth H. Betts Attorney-Cameron, Kerkam and Sutton ABSTRACTThe cushion of a gas cushion vehicle is contained by a wall structurecomprising a horizontal row of rigid members of lamellar form, e.g.,discs, mounted for independent vertical movement with respect to eachother. The lower surfaces of the members are curved to define aconvergent-divergent passage between them and the surface over which thevehicle is to operate, for the escape of gas from the cushion. Themembers are preferably enclosed in a downwardly open chamber, separatefrom the cushion space. In use, by suitably controlling the pressureabove the members, e.g., in the chamber, the. aerodynamic forces exertedon the members due to the flow of cushion gas beneath them, are arrangedto maintain the members in an equilibrium position spaced above thesurfaces over which the vehicle operates.

14 Claims, 12 Drawing Figures minimum 14 m2 SHEEI 1 [IF 6 l L I lP'A'TE'N'TEDnuv 14 I972 3.702.643

sun-. 1 2 or e PRESSURE deal/E 14/43/1698 CUSH/ON P2685025 P'A'TENTEDNov 14 m2 SHEET 5 BF 6 GAP/R MEANS FOR BOUNDING CUSHION SPACES OF GASCUSHION VEHICLES cushions of pressurized air or gas maintained in aspace, (the cushion space) beneath the vehicle or other body. Inparticular the invention is concerned with means for laterally boundinga cushion space.

' According to the invention means for laterally bounding the cushionspace of a gas cushion vehicle comprise a plurality of members of selfsustaining shape, juxtaposed in a horizontally extending row, arrangedfor independent movement in a substantially vertical plane, each memberhaving a lower surface which, together with the surface over which thevehicle is to operate, defines a potential convergentdivergent passagebeneath the member for the efflux of gas from the cushion, means beingprovided to control the downwardly acting forces exerted on the membersdue to the application thereto of pressurized gas from the cushion sothat in use, the upwardly acting forces exerted on the members due tothe efflux of gas beneath them are such that the members are normallymaintained in an equilibrium position spaced above the surface overwhich the vehicle operates.

Preferably the members comprise rigid plates or laminates having planeparallel side surfaces. Naturally the members will be placed as closelytogether as possible, to minimize the leakage of air between them,consistent with their having the required freedom of individualmovement.

The members may be mounted either for linear movement or for angularmovement in the vertical plane. In the former case the members may conveniently have the form of washers or discs loosely mounted on ahorizontally extending rod, for the desired degree of linear movement inthe vertical plane. Although it is not essential it is advantageous forthe washers to be circular so that they may rotate should they comein'contact with the surface beneath the vehicle.

In the second case, in which the members are mounted for angularmovement, they may take the form of generally pear-shaped laminatespivotall y secured on horizontal axes so as to depend from the body or aperipheral wall of the vehicle.

Preferably in order to be able to control the pressure above the membersa space or chamber, separate from the cushion space, is defined abovethe members and means are provided to control the build-up of pressurein the chamber due to flow of gas thereto from the cushion space.

The chamber above the members may be defined by a pair of dependingwalls extending parallel to the cushion boundary to embrace the members.The provision of such walls also serves in the case where the membersare in the form of dics loosely mounted on a horizontally extending rod,to restrict horizontal movement of the members at right angles to therod. In fact it may be arranged to trap the members between thedepending walls by, for example, making the walls downwardly convergent,in which event a horizontally extending rod to secure the members may bedispensed with.

The means to control the build-up of pressure in the chamber above themembers may comprise a strip of flexible material secured, for example,to the inner wall so as to prevent the direct flow of gas from thecushion to the chamber between the inner wall and the peripheries of themembers, and also to restrict flow of gas between the members to thesaid chamber. The extent to which the sealing strip masks the innerperipheries of the members which are subjected to cushion pressure maybe varied to adjust the pressure that would be built up in the chamberas required. Preferably, however, in order to control the pressure inthe space above the members, vents are provided communicating either orboth withatmosphere or the cushion space, via which leakage of gas intoand from the space may be adjusted.

Generally of course the pressure above the members must not be allowedto build up to such a value as would prevent the members from beingmaintained in the required equilibrium position, or undesirably restricttheir freedom for vertical movement. Conversely other than whenoperating to contain very low cushion pressures, it will normally benecessary to maintain thepressure above the members above atmosphericpressure.

It is to be understood that it is not essential for a cushion to belaterally bounded either to its full peripheral or vertical extent bymeans in accordance with the invention. It has already been made evidentthat the means may solely comprise a lower portion of a peripherallyextending wall, and equally of course the means of the invention may beemployed to bound only a part of the periphery of a cushion, for exampleonly at the front and rear of the vehicle, the remaining lateralboundary of the cushion being provided by other means of known form.

The invention is further described below with reference to theaccompanying drawings in which:

FIG. 1 is a diagrammatic sectional view of one embodiment of means forlaterally bounding the cushion space of a gas cushion vehicle,

FIG. 2 is an elevation of the embodiment of FIG. 1

FIG. 3 is a view corresponding to FIG. 1 of an alternative embodiment,

FIG. 4 is again similar to FIG. 1 indicating a modification of theembodiment of FIG. 1,

FIG. 5 is a plan view of an air cushion supported pallet in accordancewith the invention,

FIG. 6 is a plan view of another form of air cushion supported pallet inaccordance with the invention,

FIG. 7 is a section on the line VH VII of FIG. 6,

FIG. 8 is a graph explaining the operation of the cushion bounding meansof the invention,

FIG. 9 is a sectional view similar to FIG. 1 of a further embodiment,

. FIG. 10 is an elevation of the embodiment of FIG. 9,

FIG. 11 is a fragmentary view indicating how the cushion bounding meansof FIGS. 9 and 10 may be arranged at comers of a cushion space, and

FIG. 12 is a graph indicating the manner in which the operation of thecushion bounding means may be controlled.

Referring first to FIGS. 1 and 2, means for laterally bounding thecushion space of a gas cushion vehicle comprise a plurality ofjuxtaposed washer-like laminates 1, arranged in a horizontally extendingrow,

being loosely mounted on a rod 2. A pair of walls 3a and 3b are provideddepending from the body 4 of the vehicle to embrace the laminates 1 asshown. As indicated in FIG. 2 the laminates 1 are placed as closetogether as possible to minimize the gaps between them through which airmay leak from the cushion space 5. The laminates are not, however, soclosely packed as to restrict the laminates from being capable ofindependent movement in a vertical plane in relation to the vehicle andeach other. A flexible sealing strip 6 may be provided at the lower endof the inner wall 3b at least to restrict direct flow of air fromcushion 5 to the space or chamber 7 between the walls 3a and 3b abovethe laminates l. The space 7 may be vented to atmosphere by a series ofports 8 in the outer wall 3a, and a further series of ports 8a may beprovided in the inner wall 3b to enable the pressure in the space 7 tobe controlled as will be explained below.

Referring now to FIG. 3 an alternative form the laminates may take isindicated. Thus the laminates 1' are generally pear-shaped in outline,and are pivotally secured on horizontal axes, indicated at 9 for angularmovement in a vertical plane. In the embodiment shown the laminates arepivotally secured to the base of a stub wall 10 depending from the undersurface of the vehicle body. Equally however they may be pivoted to thelower end of a more extensive wall. A flexible sealing strip 6 may beprovided in this embodiment, as in that of FIGS. 1 and 2, to prevent thedirect flow of air from the cushion past the joint between the laminatesand the stub wall 10 and hence to the upper surface of the laminates.

The upper surfaces of the laminates 1' are enclosed by a depending wall3a defining a chamber 7 above them after the fashion of the embodimentof FIG. 1. It would be possible pivotally to connect the laminates tothe outer wall 3a rather than to the inner or stub wall 10. As in thecase of FIG. 1 ports 8 and 8a may be provided in either or both theinner and outer walls.

Referring next to FIG. 4 a modification of the embodiment of FIG. 1 isshown in which the depending walls 3a and 3b which embrace the laminates1 are formed with guide surfaces 12 which are inclined to the verticalso as to confine movement of the laminates, in the vertical plane, to anaxis correspondingly inclined to the vertical. The advantage of thisarrangement over that of FIG. 1 will be explained below.

The manner of operation of the above described arrangements is asfollows:

Initially the vehicle will be resting on the surface 13, and assuming itto be supported by the laminates, these will be positioned as indicatedin dotted lines in FIGS. 1, 3 and 4. Upon the supply of air underpressure to the cushion space 5, pressure will build up therein untilthe cushion pressure reaches the minimum value to support the weight ofthe vehicle, causing the vehicle to rise both in relation to the surface13 and the laminates l, which will then be in the position indicated infull lines. At the same time the cushion pressure will cause thelaminates to lift, to open up a gap between them and the surface 13.

Given suitable control of the pressure exerted on the upper surfaces ofthe laminates, there will be a height of the laminates above the surface13 at which the gravitational and aerodynamic forces on each laminatehave a zero component along the axis of movement provided for thelaminates in the embodiments of FIGS. 1 and 2 or 4, or a zero momentabout the pivotal connections of the laminates in the embodiment of FIG.3.

Should this height, i.e., the dimension of the gap between the lowersurface of the laminates and the surface 13 change from this equilibriumposition, due for example to undulations in the surface 13, theresultant change in the aerodynamic force will tend to move thelaminates back to the equilibrium position, i.e., the gap will bemaintained substantially constant. The gap is not significantly affectedby the magnitude of the cushion pressure, but is sensitive to the shapeof the curved lower surface of the laminates, the type of movementpermitted and to some extent the density of the laminates.

The reason for this characteristic can perhaps best be understood byconsidering extreme conditions. When the gap between the undersurface ofa laminate and the surface 13 is large, air will flow from the cushionto atmosphere through the convergent-divergent passage defined by thecurved lower surface of the laminate and the surface 13. This is similarto the flow through a venturi tube, where it is known that there is amarked reduction in static pressure at the throat. In this applicationthe marked reduction in static pressure has the effect of sucking thelaminate down towards the surface 13.

When the gap between the laminate and the surface is very small thestatic pressure drop associated with the friction between the air andthe surface at the narrowest point becomes large. Since this increasesextremely rapidly as the gap tends to zero, it follows that when thelaminate is almost touching the surface practically all the pressuredrop between the cushion and the atmosphere occurs at the narrowest partof the passage. In the limit all the pressure drop occurs at the pointof contact. In this case the inner lower part of the laminateexperiences the full cushion pressure and as a result the pressuredistribution over the laminate is such as to tend to increase the gap.

It can be shown that when the pressure above the laminates is of theright level the aerodynamic lift must vary with gap somewhat asindicated in FIG. 8, in which R is the radius of the lower surface ofthe laminate forming the convergent-divergent passage, and point E is atypical equilibrium condition which occurs when the aerodynamic lift perunit length equals the laminate weight per unit length. Precise valuesare functions of scale, atmospheric and cushion air conditions. Theequilibrium gap corresponds to a positive aerodynamic lift (or moment)balancing the negative gravitational lift (or moment).

If full cushion pressure was applied to the upper surfaces of thelaminates, the overall aerodynamic lift would of course be negative,bearing in mind that with the arrangements shown in FIGS. 1, 4 and 12pressure in the chamber 7 above the laminates acts over approximatelyhalf their circumference, whereas pressure in the cushion space 5 willact over approximately a quarter of their circumference. Hence thelaminates would be pressed down into contact with the surface beneaththem. Conversely, unless the cushion pressure was very low, if thepressure above the laminates was atmospheric pressure, the laminateswould float up to their top stops i.e., the aerodynamic lift would bepositive for all gap conditions'Hence the need, other than whenoperafing at very low cushion pressures, to adjust the equilibriumheight of the laminates above the surface over which they operate bycontrolling the pressure exerted above them. There is also the furtherfactor that with arrangements as shown in FIGS. v1 and 4, outwardlydirected forces exerted on the laminates by the cushion pressure willcause the laminates to be pressed against the outerwall 3a and tend tocause the laminates to roll up or down the wall. It must accordingly bearranged that the moment about the contact line between the laminatesand the wall is zero for the laminates to be maintained in the desiredequilibrium position.

Basically all that is required to control the pressure within thechamber 7 is to adjust the rate at which gas leaks between it and thecushion space. With the particular arrangements shown the pressure abovethe laminates needs to be maintained at a value between that ofatmospheric and approximately half the cushion pressure. The leakagerate may, as indicated at the outset, be controlled either by adjustingthe extent to which the sealing strips mask that portion of thecircumference of the laminates directly exposed to the cushion space 5,but preferably the. leakage is arranged to be controlled by means of theports 8 and 8a in'the inner and outer walls which are arranged toembrace the laminates. These ports may, of course, take a variety offorms or shapes and would normally include valve means 14 (FIG. 4) toadjust the rates of flow which could take place through them. Such meansmay be associated with the ports both in the inner and outer walls, butit may suffice to have only one of these sets of ports, preferably theinner one, controllable.

Tests have in fact indicated that with high cushion pressures laminatesmay be maintained in an equilibrium position a small distance above thesurface over which they operate by arranging for a suitable flow of gasto take place from the cushion through the ports provided in the innerwall 317 only. On the other hand, when operating at low cushionpressures, a vent needs to be provided in the outer wall instead of theinner wall. The graph of FIG. 12 generally indicates what is required.This graph in which the pressure in the chamber above the laminates,e.g., in the chamber 7, is plotted against the cushion pressure in thespace 5, indicates by the chain line the pressure which would occur inthe chamber 7 if no vents were provided in either the inner or the outerwall. Over the range of cushion pressures indicated on the left-handside of the graph, it is desirable to control the pressure in thechamber 7, as indicated by the full line, such that it is maintainedbelow the value which it would otherwise have reached, and this may beachieved by providing a vent in the outer wall. Conversely at higherpressures over the range indicated on the right-hand side of the graph,the pressure in the chamber 7 needs to be controlled so as to besomewhat higher than it would otherwise be and this may be achieved byproviding a vent in the inner wall. The graph in effect indicates thecontrol necessary with an arrangement such as described in connectionwith FIGS. 1 and 2 to maintain the laminates in an equilibrium positionspaced a constant distance above the surface over which they operate,despite variations in cushion pressure occasioned by, for example,varying loads carried by a gas cushion vehicle or pallet, the cushion ofwhich is bounded by the laminates. To achieve the required degree ofcontrol the areas of the vents in the inner or outer wall, as the casemay be, must of course be adjustable.

It is of interest to note that there appears (as indicated in FIG. 8) tobe a maximum equilibrium gap above which an infinite cushion pressurewill not lift the laminate. The nearer the equilibrium gap is to thisgap, the less sensitive will be the gap to fluctuations of cushionpressure. As the weight of the laminate tends to zero so the gap tendsto this maximum equilibrium value.

Reverting to the embodiments of FIGS. 1 to 4, that of FIGS. 1 and 2 inwhich the axis of permitted movement of the laminates is vertical, isprimarily only suitable for application where pitch or roll stabilityrequirements, and/or center of gravity variations due to varying loadsare small. The arrangements of FIGS. 3 and 4 have the advantage thatupon tilting of the vehicle body relative to the surface over which itis travelling the cushion will be laterally extended on the down-goingside due to outward angular movement of the laminates in the arrangementof FIG. 3, or upward movement along the inclined axis provided for thelaminates in the arrangement of FIG. 4. Both of these movements will ofcourse move the lowest point of the laminates horizontally outwards inrelation to the vehicle. Hence a restoring force or righting moment willbe applied to the vehicle, assisted by a corresponding inward shift ofthe opposite boundary of the cushion. A suitable angle of inclination ofthe axis of permitted movement of the laminates in the embodiment ofFIG. 4 is 30 to the vertical.

The very slight air flow between adjacent laminates is sufficient toensure that they tend to remain parallel to one another.

Although the cushion bounding means of this invention may be of use inmany applications, it is thought that they have the greatest potentialin air cushion supported pallets.

Such a pallet may be provided with simple depending side walls, arrangedif desired to run along a prepared track, the front and rear cushionboundary being provided by means in accordance with the invention.

While the laminates have very satisfactory characteristics when thedirection of movement of a vehicle is parallel to the direction in whichthe laminates are aligned, plainly when the direction of movement isotherwise, e. g., at right angles to their direction of alignment, as itwould be if they were provided at the sides of the vehicle, thelaminates may lodge on obstructions or sharp discontinuities in thesurface over which they were travelling.

This-tendency may be ameliorated by shaping the leading edge of thelaminates such that their initial slope relative to the plane of thesupporting surface is greater than the maximum local slope known tooccur on a given surface. In addition the laminates can be swept in planview, e.g., at an angle of 45 to the intended direction of travel, asindicated at the side of the pallet illustrated in FIG. 5 which isintended for travel in the direction of the arrow A. The laminates mightfurther be swept in side elevation.

With a rectangular pallet, as that of FIG. 5, in which the fullperiphery of the cushion is bounded by means in accordance with FIG. 1,it will be apparent that special provision should be made at thecorners, to provide a seal.

Stability of the pallet may be improved by compartmenting the cushionspace in known manner, as for example by the simple fixed partitionsindicated at 20. Alternatively the partitions can be flexible, e.g., beformed of bounding means in accordance with the invention.

Another form of pallet employing the cushion bounding means of theinvention is shown in FIGS. 6 and 7. In this case four cushion spacesare provided. Providing the difference between the radii of the innerand outer walls between which the laminates are held is small incomparison with the mean radius of curvature of the required cushionboundary of the or each cushion space, no excessive loss of air willoccur between the laminates.

Referring now to FIGS. 9 to 11 a further alternative form of laminate orwasher, which may be employed to form cushion bounding means inaccordance with the invention, is shown. Thus, the laminates 21 are inthe form of plates, each provided with a straight-sided slot 22 arrangedto embrace a depending wall 23. To retain the laminates in place,towards its lower end the wall 23 is provided with a shoulder, asindicated at 24, for cooperation with a complementary shoulder 25provided at the open end of the slot 22. The lower end 26 of the wallforms a close sliding fit within the slot 22, the slot being of greaterdepth than the lower part of the wall to allow the laminates to slidevertically with respect thereto to a predetermined extent. To assemblelaminates on a wall they will be slid into position from one end. Apassage 27 may be drilled through the laminates to vent the closed lowerend of the slots 22 to prevent a build up of pressure therein, such aswould restrict the required vertical movement of the laminates. Afurther passage 270 may be provided to establish communication betweenthe cushion space and the lower end of the slots 22. The passages 27 and27a can of course be arranged to serve the same function as the ports 8and 8a of the preceding embodiments. The lower ends of the laminates arecurved as indicated to provide the required potentialconvergentdivergent passage between them and the surface over which theywill operate. With this form of laminate, which will operate insubstantially the same manner as that previously described, the curve ofthe lower edges of the laminate may conveniently be made large. It isnot necessary for the laminates to be symmetrical about the wall 23.They may, for example, be shaped as indicated in chain lines. Equallythe minimum gap between the lower edges of the laminates and thesupporting surface need not be arranged to be at the midwidth of theposition of the laminates. Clearly the laminates 21 need not necessarilybe retained on the wall 23 precisely as shown. Any other suitablearrangement may be employed for this purpose.

If desired the wall 23 may be inwardly inclined so that the axis ofmovement of the laminates is inclined to the vertical to obtain thebenefit explained in connection with FIGS. 3 and 4.

With this form of washer no special provision is necessary at thecorners of a rectangular cushion space, as is the case with the washersof FIG. 1, mentioned in connection with FIG. 5. As indicated in FIG. 11the laminates bounding one side of the cushion space may be arrangeddirectly to abut laminates bounding an adjacent side.

The laminates in all the embodiments described may be made of anydesired material. Steel washers have given satisfactory results. Incertain circumstances it may be desirable to use lighter weightlaminates e. g., of aluminum or plastics material, since obviously ifthe extent of a cushion boundary to be formed by laminates or likemembers in accordance with the invention, is large, their weight mayrepresent a significant proportion of the total weight of a vehicle orpallet on which they are employed. Lighter weight laminates may alsomore rapidly respond to local variations in the surface over which theyoperate. For vehicles intended for operation over water the laminatesmay be made buoyant.

It is to be understood that the precise shape and the relativedimensions of the members or laminates is not critical, but may varywithin wide limits. The dimensions of the laminates will be determinedamongst other factors by the dimensions of obstacles they are designedto negotiate.

It will be seen that a cushion boundary formed by means in accordancewith the invention, will generally act in a manner similar to flexibleskirts, in so far as their ability to negotiate obstacles and to conformwith surface contours is concerned. The members or laminates are ofcourse independently deflectable as are the members of segmented"skirts.

Because the members or laminates will normally be maintained out ofcontact with the surface, wear due to occasional contact therewithshould not be severe, particularly bearing in mind the relatively robustnature of the laminates compared with for example flexible materialcommonly used for the manufacture of skirts.

While the cushion bounding means of this invention have only beendescribed as providing a seal with a substantially horizontal surfaceover which a vehicle fitted with them may travel, they may equally ifdesired be arranged to provide a seal with vertical or inclinedsurfaces, for example the walls of a channel along which an air cushionsupported pallet may be arranged to run.

Air cushion vehicles and particularly air cushion pallets with flexibleskirts are prone to suffer from instability in heave unless the rate ofsupply of air to the cushion and the cushion pressure are very low. Thebasic cause of this instability is the discontinuity in the rate ofleakage (plenum leak) which occurs beneath the cushion containingskirts.

Varying the height of the skirt around its periphery will result inplenum leak varying smoothly over a range of hover heights correspondingto the range of skirt heights. With cushion bounding means in accordancewith the present invention this can readily be achieved by employinglaminates of different dimensions to form a cushion boundary. It isbelieved, however, that heave instability may better be countered byarranging for an increase in the rate of plenum leakage as a vehiclerises to a predetermined equilibrium position or hover height.

With cushion bounding means in accordance with the present invention therequired control of plenum leakage may conveniently be provided for bysuitably positioning the ports 8a provided in the inner wall definingthe chamber 7 in the embodiments of FIGS. 1, 3 and 4. Thus these portsmay be positioned so that they are sealed by the laminates when theseare in the chain dotted position, but are progressively opened as thevehicle rises. It can then be arranged for the vehicle to be inequilibriumbefore the laminates reach their fully extended position,i.e.,,it will be arranged that when the laminates are fullyextended theleak rate is greater than the supply rate. If desired, venting of thespace 7 via the ports 8 may equally be arranged to be controlled by thelaminates.

It will be appreciated that this ancillary function of the ports 8 and8a must not be allowed to disturb their main function of controlling thepressure exerted above the laminates. Thus the total area for leakagethrough the inner and outer walls 3a and 3b, and its variation with theposition of the laminates relative to these walls should be kept at aminimum consistent with obtaining satisfactory stability. It remainsnecessary to control the ratio of leakage into the chamber 7 to theleakage out of the chamber to ensure that the laminates may bemaintained in the required equilibrium position above the surface overwhich they operate. The pressure in the space 7 must of course bemaintained at a value which causes the skirt to float at the desiredheight above the supporting surface.

With the alternative form of laminate described in connection with FIG.9 appropriately controlled venting of the cushion space as the vehiclerose could be arranged to take place via vents as indicated at 28. Asindicated in FIG. 10the number, size and position of vents controlled byeach individual laminate may be varied in a random or predeterminedmanner to give the vehicle or pallet concerned the requiredcharacteristic. Instead of providing a plurality of aligned vents to becontrolled by each laminate it may be more convenient to provide asingle elongated vent in the wall 23 aligned with each laminate.

In certain cases it may be unnecessary to provide ventilating slots orports in the wall 23. The gaps between the laminates may be such as togive sufficient leakage variation with height to ensure adequatestability in heave.

I claim:

1. Means for bounding, at least in part, the periphery of a cushionspace of a gas cushion supported apparatus, the said means comprising aplurality of members of self-sustaining shape, juxtaposed in ahorizontally extending row, arranged for independent movement in asubstantially vertical plane, each member having a surface which definesa potential convergentdivergent passage between the said member and thesurface over which the apparatus is to be supported for the efflux ofgas from the cushion wherein the pressure of the gas is maintained aboveatmospheric pressure, means being provided to control downwardly actingforces exerted on the members due to the application thereto ofpressurized gas from the cushion so that, in use, upwardly acting forcesexerted on the members due to the said efflux of gas are such that themembers are normally maintained in an equilibrium position spaced fromthe said surface.

2. Means for bounding, at least in part, the periphery of a cushionspace of a gas cushion supported apparatus, the said means comprising aplurality of members of self-sustaining shape, juxtaposed in ahorizontally extending row, arranged for independent movement in asubstantially vertical plane, each member having a surface which definesa potentially convergent-divergent passage between the said member andthe surface over which the apparatus is to be supported for the effluxof gas from the cushion, defining above the said members a space orchamber, separate from the said cushion space, including means tocontrol the build-up of pressure in the chamber due to the flow of gasthereto from the cushion space, so as to maintain the pressure thereinat a value between that of atmosphere and about half cushion pressure,so that, in use, upwardly acting forces exerted on the members due tothe said efflux of gas are such that the members are normally maintainedin an equilibrium position spaced from the said surface.

3. Means as claimed in claim 1 in which the said members comprise rigidplates having plane parallel side surfaces, each member being formedwith a slot slidably engaging the free end of a wall structure fromwhich the members are arranged to depend.

4. Means as claimed in claim 2 in which the said members comprise rigidplates having plane parallel side surfaces, the members being mountedfor angular movement in the vertical plane with respect to the vehicle.

5. Means as claimed in claim 2 in which the said chamber is defined byinner and outer wall structures between which the said members aremounted.

6. Means as claimed in claim 5 in which the members are in the form ofdiscs loosely mounted for linear movement in the vertical plane on ahorizontally extending rod.

7. Means as claimed in claim 5 in which the said members comprise rigidplates having plane parallel side surfaces, the members being mountedfor angular movement in the vertical plane with respect to the vehicle.

8. Means for bounding, at least in part, the periphery of a cushionspace of a gas cushion supported apparatus, the said means comprising aplurality of members of self-sustaining shape, juxtaposed in ahorizontally extending row, said members comprising rigid plates havingplane parallel side surfaces and being mounted for independent linearmovement in a vertical plane with respect to the vehicle, each memberhaving a surface which defines a potential convergent-divergent passagebetween the said member and the surface over which the apparatus is tobe supported for the efflux of gas from the cushion, means beingprovided to control downwardly acting forces exerted on the members dueto the application thereto of pressurized gas from the cushion so that,in use, upwardly acting forces exerted on the members due to the saidefflux of gas are such that the members are normally maintained in anequilibrium position spaced from the said surface.

9. Means for bounding, at least in part, the periphery of a gas cushionof a gas cushion supported apparatus, the said means comprising aplurality of members of self-sustaining shape and lamellar form,juxtaposed in a horizontally extending row, and arranged for independentrelative movement in a substantially vertical plane, each member havinga lower surface which, together with the surface over which theapparatus is to be supported, defines a potential convergent-divergentpassage beneath the member for the efi'lux of gas from the cushion, themembers being enclosed between depending inner and outer wall structuresdefining a downwardly open chamber, separate from the cushion space,means being provided to control the build up of pressure in the chamberabove the members due to leakage of gas thereto from the cushion, so asto maintain the pressure therein at such a value that, in use, forcesexerted on the members due to the said efflux of gas normally maintainthe members in an equilibrium position spaced above the surface overwhich the apparatus is supported.

10. A gas cushion vehicle in which the vehicle-supporting cushion iscontained, at least in part, by a wall structure depending from thevehicle body, the wall structure comprising a plurality of members ofselfsustaining shape and lamellar form, contiguously arranged in ahorizontally extending row, means 'rnounting the members so as to dependfrom the body for independent relative movement in a substantiallyvertical plane with respect thereto, the members having a convex surfaceto define, in use, with the surface over which the vehicle is tooperate, a convergent-divergent passage for the efflux of gas from thecushion wherein the pressure of the gas is maintained above atmosphericpressure, means being provided to restrict flow of gas from the cushionto the upper surface of the members, operative to maintain the pressureabove the members at a value less than that of the cushion pressure butabove atmospheric pressure, so that forces exerted on the members due tothe said efflux of gas beneath them, normally maintain the members in anequilibrium position spaced above the surface over which the vehicleoperates.

11. A gas cushion vehicle in which the vehicle-supporting cushion iscontained, at least in part, by a wall structure depending from thevehicle body, the wall structure comprising a plurality of members ofselfsustaining shape and lamellar form, contiguously arranged in ahorizontally extending row, means mounting the members so as to dependfrom the body for independent relative movement in a substantiallyvertical plane with respect thereto, the members having a convex surfaceto define, in use, with the surface over which the vehicle is tooperate, a convergent-divergent passage for the efflux of gas from thecushion, means being provided to restrict flow of gas from the cushionto the upper surface of the members, operative to maintain the pressureabove the members at a value less than that of the cushion pressure, sothat forces exerted on the members due to the said efflux of gas beneaththem, normally maintain the members in an equilibrium position spacedabove the surface over which the vehicle operates, and inner and outerwalls depending from the vehicle body, between which walls the saidmembers are mounted and defining above the members a chamber, gas ventsbeing provided in at least one of said inner and outer walls to providefor a controlled leakage of gas from the cushion through the saidchamber to maintain the pressure in the said chamber at the requiredvalue.

12. A gas cushion vehicle as claimed in claim 11 in which the memberscomprise discs mounted so as to be free to rotate upon contacting thesurface over which the vehicle operates.

13. A gas cushion vehicle as claimed in claim 12 in which it is arrangedfor the discs only to be directly subjected to cushion pressure overtheir inner lower quadrant and the pressure in the said chamber ismaintained at a pressure between that of atmosphere and half cushionpressure.

14. A gas cushion vehicle as claimed in claim 11 including means forvarying the rate of said controlled leakage from the cushion independence upon the hoverheight of the vehicle, the means beingoperative to increase the rate of leakage as the vehicle rises to apredetermined hoverheight.

1. Means for bounding, at least in part, the periphery of a cushion space of a gas cushion supported apparatus, the said means comprising a plurality of members of self-sustaining shape, juxtaposed in a horizontally extending row, arranged for independent movement in a substantially vertical plane, each member having a surface which defines a potential convergentdivergent passage between the said member and the surface over which the apparatus is to be supported for the efflux of gas from the cushion wherein the pressure of the gas is maintained above atmospheric pressure, means being provided to control downwardly acting forces exerted on the members due to the application thereto of pressurized gas from the cushion so that, in use, upwardly acting forces exerted on the members due to the said efflux of gas are such that the members are normally maintained in an equilibrium position spaced from the said surface.
 2. Means for bounding, at least in part, the periphery of a cushion space of a gas cushion supported apparatus, the said means comprising a plurality of members of self-sustaining shape, juxtaposed in a horizontally extending row, arranged for independent movement in a substantially vertical plane, each member having a surface which defines a potentially convergent-divergent passage between the said member and the surface over which the apparatus is to be supported for the efflux of gas from the cushion, defining above the said members a space or chamber, separate from the said cushion space, including means to control the build-up of pressure in the chamber due to the flow of gas thereto from the cushion space, so as to maintain the pressure therein at a value between that of atmosphere and about half cushion pressure, so that, in use, upwardly acting forces exerted on the members due to the said efflux of gas are such that the members are normally maintained in an equilibrium position spaced from the said surface.
 3. Means as claimed in claim 1 in which the said members comprise rigid plates having plane parallel side surfaces, each member being formed with a slot slidably engaging the free end of a wall structure from which the members are arranged to depend.
 4. Means as claimed in claim 2 in which the said members comprise rigid plates having plane parallel side surfaces, the members being mounted for angular movement in the vertical plane with respect to the vehicle.
 5. Means as claimed in claim 2 in which the said chamber is defined by inner and outer wall structures between which the said members are mounted.
 6. Means as claimed in claim 5 in which the members are in the form of discs loosely mounted for linear movement in the vertical plane on a horizontally extending rod.
 7. Means as claimed in claim 5 in which the said members comprise rigid plates having plane parallel side surfaces, the members being mounted for angular movement in the vertical plane with respect to the vehicle.
 8. Means for bounding, at least in part, the periphery of a cushion space of a gas cushion supported apparatus, the said means comprising a plurality of members of self-sustaining shape, juxtaposed in a horizontally extending row, said members comprising rigid plates having plane parallel side surfaces and being mounted for independent linear movement in a vertical plane with respect to the vehicle, each member having a surface which defines a potential convergent-divergent passage between the said member and the surface over which the apparatus is to be supported for the efflux of gas from the cushion, means being provided to control downwardly acting forces exerted on the members due to the application thereto of pressurized gas from the cushion so that, in use, upwardly acting forces exerted on the members due to the said efflux of gas are such that the members are normally maintained in an equilibrium position spaced from the said surface.
 9. Means for bounding, at least in part, the periphery of a gas cushion of a gas cushion supported apparatus, the said means comprising a plurality of members of self-sustaining shape and lamellar form, juxtaposed in a horizontally extending row, and arranged for independent relative movement in a substantially vertical plane, each member having a lower surface which, together with the surface over which the apparatus is to be supported, defines a potential convergent-divergent passage beneath the member for the efflux of gas from the cushion, the members being enclosed between depending inner and outer wall structures defining a downwardly open chamber, separate from the cushion space, means being provided to control the build up of pressure in the chamber above the members due to leakage of gas thereto from the cushion, so as to maintain the pressure therein at such a value that, in use, forces exerted on the members due to the said efflux of gas normally maintain the members in an equilibrium position spaced above the surface over which the apparatus is supported.
 10. A gas cushion vehicle in which the vehicle-supporting cushion is contained, at least in part, by a wall structure depending from the vehicle body, the wall structure comprising a plurality of members of self-sustaining shape and lamellar form, contiguously arranged in a horizontally extending row, means mounting the members so as to depend from the body for independent relative movement in a substantially vertical plane with respect thereto, the members having a convex surface to define, in use, with the surface over which the vehicle is to operate, a convergent-divergent passage for the efflux of gas from the cushion wherein the pressure of the gas is maintained above atmospheric pressure, means being provided to restrict flow of gas from the cushion to the upper surface of the members, operative to maintain the pressure above the members at a value less than that of the cushion pressure but above atmospheric pressure, so that forces exerted on the members due to the said efflux of gas beneath them, normally maintain the members in an equilibrium position spaced above the surface over which the vehicle operates.
 11. A gas cushion vehicle in which the vehicle-supporting cushion is contained, at least in part, by a wall structure depending from the vehicle body, the wall structure comprising a plurality of members of self-sustaining shape and lamellar form, contiguously arranged in a horizontally extending row, means mounting the members so as to depend from the body for independent relative movement in a substantially vertical plane with respect thereto, the members having a convex surface to define, in use, with the surface over which the vehicle is to operate, a convergent-divergent passage for the efflux of gas from the cushion, means being provided to restrict flow of gas from the cushion to the upper surface of the members, operative to maintain the pressure above the members at a value less than that of the cushion pressure, so that forces exerted on the members due to the said efflux of gas beneath them, normally maintain the members in an equilibrium position spaced above the surface over which the vehicle operates, and inner and outer walls depending from the vehicle body, between which walls the said members are mounted and defining above the members a chamber, gas vents being provided in at least one of said inner and outer walls to provide for a controlled leakage of gas from the cushion through the said chamber to maintain the pressure in the said chamber at the required value.
 12. A gas cushion vehicle as claimed in claim 11 in which the members comprise discs mounted so as to be free to rotate upon contacting the surface over which the vehicle operates.
 13. A gas cushion vehicle as claimed in claim 12 in which it is arranged for the discs only to be directly subjected to cushion pressure over their inner lower quadrant and the pressure in the said chamber is maintained at a pressure between that of atmosphere and half cushion pressure.
 14. A gas cushion vehicle as claimed in claim 11 including means for varying the rate of said controlled leakage from the cushion in dependence upon the hoverheight of the vehicle, the means being operative to increase the rate of leakage as the vehicle rises to a predetermined hoverheight. 